A plasma processing apparatus is constructed to perform processes (e.g., etching, deposition, oxidation and sputtering) on a target substrate (e.g., a semiconductor wafer, a glass substrate for use in FPD or the like) in a hermetically sealable processing chamber serving as a vacuum chamber. In a single-wafer capacitively coupled plasma processing apparatus that is now widely in use, an upper and a lower electrode are disposed in parallel, and a substrate is mounted on the lower electrode. Further, a radio frequency is applied to at least one of the electrodes while supplying a processing gas to a space between the electrodes. Electrons are accelerated by a radio frequency electric field formed between the electrodes by the application of the radio frequency, and a plasma is generated by ionization caused by collision of the electrons and the processing gas. Then, a required treatment or microprocessing is performed on a surface of the substrate by radicals or ions in the plasma.
In the above plasma processing apparatus, gaseous reaction products or reaction by-products generated during the plasma processing are adhered to some parts in the processing chamber (especially surfaces of plasma-facing parts), and become solidified there as deposits. The plasma-facing parts in the processing chamber are usually as follows: a bottom surface of the upper electrode, a top surface of a peripheral portion of the lower electrode (susceptor) that encloses the substrate, a sidewall of the processing chamber and the like.
Besides, if the processing chamber is configured such that the upper electrode forms a united body with a ceiling of the processing chamber, a supporting member at the periphery of the upper electrode and the surface of the ceiling are also included in the plasma-facing parts. Moreover, in case of a configuration in which a ring-shaped focus ring larger than a substrate is installed on a top surface of the susceptor, or in which an outer peripheral surface of the susceptor is surrounded by a cylindrical wall, the focus ring or the wall is also included in the plasma-facing parts (see, e.g., Patent Document 1).
When the deposits adhered to the surfaces of the plasma-facing parts are removed due to, e.g., a separation of a film, the deposits become particles, thereby deteriorating a production yield. To avoid this problem, the deposits are removed from each part of the processing chamber by performing a cleaning process regularly or when necessary.    (Patent Document 1) Japanese Patent Application Publication No. 2001-93884
In the above plasma processing apparatus, it is required that, if two different parts that face the plasma space inside the processing chamber are adjoined to each other, an appropriate space or gap should be formed therebetween for the purpose of absorbing thermal expansion, preventing an electric conduction therebetween and an unwanted stress therebetween and the like. For example, when the disk-shaped upper electrode serving as a shower head for introducing a processing gas is to be attached to the ceiling of the processing chamber via a ring-shaped supporting member, an inner diameter of the supporting member is set slightly larger than an outer diameter of the upper electrode so that a gap can be formed between an outer peripheral surface of the upper electrode and an inner peripheral surface of the supporting member. Further, when the upper electrode is to be divided in a radial direction into an inner circular plate-shaped electrode and an outer ring-shaped electrode, a space may be formed therebetween in consideration of the above.
However, if a gap exists between the two plasma facing parts, deposits may enter the gap to thereby cause particle-related problems. In general, to remove the particles having entered a gap in the processing chamber, a manual cleaning does not work, and a gas cleaning or plasma cleaning is required. Especially in case of such a gap that faces the plasma space, the plasma cleaning is effective in that it takes advantage of ion sputtering effect. However, in a conventional plasma processing apparatus, if a joining portion of two plasma facing parts is angled or stepped, ions hardly enter the gap therebetween so that deposits in the gap is difficult to be removed even by the plasma cleaning.